Linear oscillating motor

Abstract

A linear oscillating motor capable of assuring a consistent and effective feedback control of keeping a constant oscillation amplitude with varying load conditions. The linear oscillating motor comprises an oscillator carrying a permanent magnet, and a stator with an electromagnet. The electromagnet is supplied with an electric power to develop an electromagnetic drive force of moving the oscillator in a linear direction relative to the stator. A spring is provided to apply a restoring force to the oscillator for providing a linear oscillating motion to the oscillator. A photo-sensor monitors the linear motion of the oscillator and outputs a signal to a reverse-point detector which determines right and left reverse points of the oscillator. A controller applies the electric power to the electromagnet at the drive points respectively defined subsequent in time to the reverse points and in a varying amount for keeping a constant oscillation amplitude of the oscillator. The photo-sensor outputs a train of pulses appearing each time the oscillator passes its oscillation center. The reverse-point detector determines the reverse points based upon a time period between the two preceding pulses. Since the photo-sensor can monitor an oscillation cycle of the oscillator without being affected by the magnetic field developed by the electromagnet for driving the oscillator, it provides a reliable basis for accurately determining the reverse points and therefore the drive points. Accordingly, the driving force can be applied at an optimum timing to make the feedback control accurately and reliably.